Phineas and Ferb (2007)

S3E9 Misperceived Monotreme

Perry is unable to participate in his 100th showdown with Dr. Doofenshmirtz because Candace brings him along to the Charity Pet Wash. Unbeknownst to everyone, the usual platypus at the Danville Zoo intervenes to thwart Dr. Doofenshmirtz's scheme to zap his brother with the "Least Likely-inator." Meanwhile, Phineas and Ferb are busy constructing a whimsical fun house, showcasing their signature creative flair.